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Bellows Movements and Spring Rates Movement Capabilities

There are four basic movements that can be applied to a bellows. These are Axial, Lateral, Angular and Torsional. Figures 1

through 5 illustrate these movements. Bellows be have like springs in a piping system. When they are compressed, the

bellows resist the movement the same as a spring would. The spring rate of a bellows is entirely dependant on bellows

geometry and material properties. Macoga is able to vary bellows geometry such as convolution height, pitch, thickness and

number of plies to provide a bellows to satisfy any customer’s needs.

Axial Movement (+/‐‐‐‐ mm)

Axial movement is the change in dimensional length of the bellows from its free length in a direction parallel to its

longitudinal axis. Compression is always expressed as negative (‐) and extension as positive (+). The units for axial

spring rates displayed in N/mm.

Angular Movement ( +/‐‐‐‐ Degrees )

Angular movement is the rotational displacement of the longitudinal axis of the bellows toward a point of rotation.

The convolutions at the inner most point are in compression (‐) while those furthest away are in extension (+). The angular

capability of a bellows is most often used with a second bellows.

The units for angular spring rates displayed in Nm/deg

Lateral Movement (+/‐‐‐‐ mm)

Lateral movement is the relative displacement of one end of the bellows to the other end in a direction perpendicular to

its longitudinal axis (shear). Lateral movement can be imposed on a single bellows as depicted below but to a limited degree.

A better solution is to incorporate two bellows in a universal arrangement as shown. This results in greater offset movements

and much lower offset forces.

The units for lateral spring rates displayed in N/mm

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Torsional Movement (+/‐‐‐‐ Degrees)

Torsional movement is the rotation about the axis through the center of a bellows (twisting). Macoga DISCOURAGES

ANY TORSIONAL ROTATION OF METAL BELLOWS EXPANSION JOINTS. Torsion destabilizes an expansion joint

reducing its ability to contain pressure and absorb movement. If torsion is present in a piping system, hinges, slotted hinges

or gimbals are recommended to combat the torsion. Torsional spring rates are in Nm/deg and maximum torsional limits in

degrees for computational modeling only. Piping software such as CAESAR II and COADE often require these spring rates for

nodal input.

Pressure thrust is the force created by pressure acting on a bellows. This force is the system pressure times the effective area

of the bellows. When a piping system without expansion joints is pressurized, the system will not move because the pipe is

countering the force in tension. When an unrestrained expansion joint is introduced in the network, the force tends to pull

the ends away from the expansion joint causing damage to itself and the pipe. This pressure thrust must be contained with

either main anchors or restrained expansion joints designed to carry pressure thrust loads. The main anchors must be able to

resist the pressure thrust force and a small amount of force due to the deflection of the bellows.

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Example: Pipe size = 12” nominal

P = System Pressure = 300 psig

A = Effective Area of 12” part = 151 in2

= Pipe growth between anchors = 0.5 in compression

SR = Axial Spring Rate of the 12” part = 6,255 Lbs/in

First find the force due to the pressure: PRESSURE THRUST = P X A = 300 psig X 151 in2 = 45,300 Lbs

Next find the force due to the bellows deflection:

BELLOWS SPRING FORCE = X SR = 0.5 in X 6,255 Lbs/in = 3,128 Lbs

The main anchors must resist the sum of these two forces: PRESSURE THRUST + BELLOWS SPRING FORCE = 45,300 Lbs + 3,128 Lbs = 48,428 Lbs

Basic Types of Expansion Joints Unrestrained Assemblies Definition: Assemblies not capable of restraining the pressure thrust of the system. The pressure thrust must be contained

using main anchors or equipment.

Single Bellows

The simplest type of expansion joint consists of a single

Bellows element welded to end fittings, normally flange

or pipe ends. The single bellows can absorb small

amounts of axial, lateral and angular movement with

ease, but adequate anchors and guides must be provided.

Universal Expansion Joint

This expansion joint consists of two bellows connected by

a center spool piece with flange or pipe ends. The universal

arrangement allows greater axial, lateral and angular

movements than a Single Bellows . Increasing the center

spool length produces increased movement capability.

Like the single, adequate anchors and guides must be

provided.

Externally Pressurized Expansion Joint

Line pressure acts externally on the bellows by means of a

Pressure chamber. This allows a greater number of convolutions

to be used for large axial movements, without fear of bellows

instability. Externally Pressurized Expansion Joints have the

added benefit of self‐draining convolutions if standing media

is a concern. Anchors and guides are an essential part of a

good installation.

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Restrained Assemblies Definition: Assemblies capable of restraining the pressure thrust of the system. Intermediate anchors are required to

withstand

the spring force generated when the expansion joint is deflected. The need for main anchors is eliminated

Tied Single Bellows

The addition of tie rods to a Single Bellows Assembly adds design

flexibility to a piping system. The tie rods are attached to the pipe

or flange with lugs that carry the pressure thrust of the system,

eliminating the need for main anchors. With the assembly tied,

the ability to absorb axial growth is lost. Only lateral and angular

movement can be absorbed with the tied expansion joint. The

addition of tie rods does not eliminate the need for a well‐planned

guide system for the adjacent piping.

Tied Universal Expansion Joint

Similar in construction to a Universal Assembly except that tie rods

absorb pressure thrust and limit movements to lateral offset and

angulation. Large offset movements are possible in a Universal

Assembly by increasing the distance between the two bellows.

Hinged Expansion Joint

When a Hinged Expansion Joint is used, movement is limited to

Angulation in one plane. Hinged Assemblies are normally used in

sets of two or three to absorb large amounts of expansion in high

pressure piping systems. Only low spring forces are transmitted to

the equipment. The hinge hardware is designed to carry the pressure

thrust of the system, and often times, used to combat torsional

movement in a piping system. Slotted Hinged Expansion Joints are

a variant of the standard Hinged Expansion Joints that allow axial

and angular movement. Important note: Once a Slotted Hinge is

introduced, torsion in the piping system is still resisted but the

hinge no longer carries pressure thrust.

Gimbal Expansion Joint

The gimbal restraint is designed to absorb system pressure thrust

And torsional twist while allowing angulation in any plane. Gimbal

Assemblies, when used in pairs or with a Single Hinged unit, have the

advantage of absorbing movements in multi‐planer piping systems.

The gimbal works the same as an automobile's universal drive shaft.

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Pressure Balanced Elbow Expansion Joint:

These assemblies are used in applications where space

limitations preclude the use of main anchors. Pressure thrust

acting on the line bellows (bellows in the media flow) is

equalized by the balancing bellows through a system of tie

rods or linkages. The only forces transmitted to equipment are

low spring forces created by the axial, lateral, or angular

movements. An elbow must be present in the piping network

to install this style of expansion joint.

In‐‐‐‐Line Pressure Balanced Expansion Joint:

If an elbow is not present in a piping network and pressure thrust

Must be absorbed by the expansion joint, an In‐Line Pressure

Balanced expansion joint is the solution. An equalizing bellows

with twice the effective area as the line bellows is tied in the

expansion joint through a series of tie rods. The opposing

pressure forces cancel each other leaving only the low spring

forces generated from the bellows deflection.

Externally Pressurized Pressure Balanced Expansion Joint:

If large amounts of axial movement in a system are needed and

the expansion joint must absorb pressure thrust, an Externally

Pressurized Pressure Balanced expansion joint is the solution.

The opposing force balancing theory is similar to the In‐Line

Pressure Balanced Assembly except the opposing forces are

generated from pressure acting on the outside of the bellows.

END CONNECTIONS & ACCESSORIES Flanges

Any flange style can be added to a bellows for bolting into

a system. Forged steel or plate flanges to match the

pressure and temperature ratings of ANSI Class 150 or

ANSI Class 300 are standard

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Vanstone Ends

Vanstone ends are modified flanged ends with the added

flexibility for resolving bolt‐hole misalignment or wetted

surface corrosion.

Weld Ends

Any pipe or duct can be attached to a bellows for welding

into a system. Pipe in accordance with ASTM A53 Gr. B or

A106 Gr. B is used for standard sizes 3 in. to 24 in. nominal

diameter. Plate to ASTM A36 or A516 Gr. 70 rolled and

welded is used for custom sizes 26 in. diameter.

Stainless steel or other alloy pipe can also be

provided.

Liners (Internal Sleeves)

when any of the following conditions exist:

A. When pressure drop must be minimized and smooth flow is

essential.

B. When turbulent flow is generated upstream of the expansion

joint by changes in flow direction.

C. When it is necessary to protect the bellows from media

carrying abrasive materials such as catalyst or slurry.

D. In high temperature applications to reduce the temperature

of the bellows. The liner is a barrier between the media and the

bellows.

E. For Air, Steam and other Gases

Up to 6 in. diameter ‐ 4 ft/sec/in. of diameter

Over 6 in. diameter ‐ 25 ft/sec.

For Water and other Liquids

Up to 6 in. diameter ‐ 2 ft/sec/in. of diameter

Over 6 in. diameter ‐ 10 ft/sec.

Flow liners can trap liquid if the expansion joint is installed with

the flow vertical up. On this case the internal sleeve are provided with

drain holes to prevent liquid buildup under the liner. For custom

designs, flow direction should always be provided.

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Protective Covers and Shrouds

Covers and shrouds can be provided either fixed or

removable. Fixed types are used where high velocity

external steam conditions exist such as in condenser

heater connections. The removable type is the Macoga

standard and permits periodic in service inspection.

They are also used to prevent damage

during installation and operation or when welding is

going to be performed in the immediate vicinity. If

the expansion joint is going to be externally insulated,

a cover should be considered. Macoga always recommends

covers for any expansion joint. The small cost increase

is just economical insurance when compared to a

complete joint replacement.

Tie Rods

Ties rods are devices, usually in the form of bars or rods,

attached to the expansion joint assembly and are designed

to absorb pressure loads and other extraneous forces like

dead weight. When used on a Single or Universal Style

Expansion Joint, the ability to absorb axial movement is lost.

Limit Rods

Limit rods are used to protect the bellows from movements

in excess of design that occasionally occurs due to plant

malfunction or the failure of an anchor. LIMIT RODS DO NOT

CONTAIN THE PRESSURE THRUST DURING NORMAL

OPERATION. Limit rods are designed to prevent bellows

over‐extension or over‐compression while restraining the full

pressure loading and dynamic forces generated by an anchor

failure. During normal operation the rods have no function.

Purge Connections

Purge connections are used in conjunction with internal liners

to lower the skin temperature of the bellows in high

temperature applications such as catalytic cracker bellows.

The purge media can be air or steam which helps flush out

particulate matter between bellows and the liner. This also

prevents the build up of harmful solids in the convolutions

that may stop the bellows from performing.

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MATERIAL SELECTION GUIDELINES Bellows Material Selection of the bellows material is the single most important factor to be considered in the design of an expansion joint.

Some of the factors, which influence the selection process, are as follows:

Factors Considerations

Corrosion Properties Process media

Surrounding environment

Internal cleaning agents

Mechanical Properties High temperature service

Cryogenic service

Operating stresses

Manufacturing properties Forming and cold working capabilities

BELLOWS MATERIAL Stainless Steel‐‐‐‐ Type 300 austenitic series

304 (ASTM A240‐‐‐‐304)

Services a wide range of applications. It resists organic chemicals, dye stuff, and a wide variety of inorganic chemicals. Type

304 resists nitric acid and sulfuric acids at moderate temperatures and concentrations. It is used extensively in piping systems

conveying petroleum products, compressed air, steam, flue gas, and liquefied gases at cryogenic temperatures. The

temperature range varies from ‐324 to 1200 degrees F.

304L (ASTM A‐‐‐‐240‐‐‐‐304L)

Has a maximum carbon content of 0.03% versus 0.08% for type 304. This lower carbon content eliminates the problem of

chromium carbide precipitation and makes it more resistant to intergranular corrosion. It is preferred over 304 for nitric acid

service.

316 (ASTM A‐‐‐‐240‐‐‐‐316)

This alloy contains more nickel than the 304 types. The addition of 2% to 3% molybdenum gives it improved corrosion

resistance compared to 304 especially in chloride environments that tend to cause pitting. Some typical uses are flue gas

ducts, crude oil systems high in sulfur, heat exchangers, and other critical applications in the chemical and petrochemical

industries.

316L (ASTM A‐‐‐‐240‐‐‐‐316L)

With its low carbon content of 0.03% maximum, it lends itself to highly corrosive applications where intergranular corrosion

is a hazard.

321 (ASTM A240‐‐‐‐321)

The addition of titanium to this stainless steel acts as a carbide stabilizing element that prevents carbide precipitation when

the material is heated and cooled through the temperature range of 800 to 1650 degrees F. 321 finds uses in many of the

same applications as Type 304, where the added safeguard from intergranular corrosion is desired. The standard catalog

exhaust joints are made from this material because of the high operating temperatures they withstand.

Nickel Alloys

Nickel 200 (ASTM B162‐‐‐‐200)

A commercially pure nickel (99.5% Ni), nickel 200 has good mechanical properties and excellent corrosion resistance to salt

water attack and chloride cracking.

Alloy 400 (ASTM B127‐‐‐‐400)

This copper‐nickel alloy (66.5% Ni, 31.5 Cu) is a higher strength material than Nickel 200 with excellent corrosion resistance

over a wider range of temperatures and operating conditions.

Alloy 600 (ASTM B168‐‐‐‐600)

This nickel‐chromium alloy (76% Ni, 15.5% Cr) has very desirable properties for the manufacture of expansion joints. It has a

very high strength over a wide range of temperatures and a good resistance to a variety of corrosive environments. It finds

wide use in steam and salt water services where it is virtually immune to chloride stress corrosion.

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Alloy 625 Gr.1 (ASTM B443‐‐‐‐625)

This alloy contains a higher chromium content (21.5%) than alloy 600. With the addition of 9% molybdenum, it produces an

alloy of superior strength and corrosion resistance over a wider range of temperatures and environments. It is used on many

critical applications such as heat exchangers and catalytic cracker expansion joints. When exposed to temperatures above

1000 deg F for prolonged periods, it may become embrittled.

Alloy 625 LCF (ASTM B443‐‐‐‐625 LCF)

Similar to straight grade 625, this alloy has a slight change in material composition to enhance low‐cyclic fatigue properties at

elevated temperatures.

Alloy 800 (ASTM B409‐‐‐‐800)

This nickel‐iron‐chrome alloy is less expensive than alloy 600. It has good corrosion resistance properties and high

temperature strength over a wide variety of difficult service conditions.

Alloy 825 (ASTM B424‐‐‐‐825)

This is a copper‐chrome nickel alloy that exhibits excellent corrosion resistance to the most severe acids, in particular hot

concentrated sulfuric acid and sulfur bearing environments.

Alloy 20 or 20Cb‐‐‐‐3 (ASTM B463)

This nickel‐iron‐chrome alloy was specifically designed to resist hot sulfuric acid. It is able to resist intergranular corrosion in

the aswelded condition and is practically immune to chloride stress corrosion cracking.

Other Materials In addition to the materials listed above, Macoga has successfully manufactured bellows from Hastelloy C22 and C276,

Corten, AL6XN, duplex 2205, alloys 230, 253 MA, 330, 617, 718, 800H/HT, 3CR12, HR120 and others. Many grades of “SA”

and “SB” materials are stocked for expansion joints requiring ASME partial data reports. Please consult Macoga for any

material not listed or for ordering catalog parts with alternate materials Macoga manufactures bellows from mill‐annealed

material only and no annealing is performed after the forming process is complete. Macoga must know if the customer

requires annealing of the material after forming. Occasionally, annealing will enhance material properties or corrosion

resistance. Macoga discourages post‐formed annealing because it hinders the bellow’s ability to contain pressure and may

also lower cycle life.

Shipping & Handling Every expansion joint that leaves the factory is provided with

installation instructions. These instructions describe the simple,

straightforward requirements that must be followed to insure a

trouble‐free installation.

Shipping Bars ‐ These are temporary attachments that "hold" the

expansion joint at its correct installed length during shipping and

installation. Angle iron or channel section is used and is always

painted bright yellow. Shipping bars must never be removed until

after the unit has been correctly welded or bolted into the piping

system. Caution: Tie rods or limit rods are sometimes mistaken

for shipping bars. NEVER TAMPER WITH THESE ATTACHMENTS.

NOTE: Great care must be taken when removing the shipping

bars. If a welding or burning torch is used, ALWAYS protect the

bellows element from burn splatter with a flame‐retardant cloth

or other shielding material.

Liners ‐ When expansion joints are fitted with liners or internal

sleeves, the unit is marked with an arrow indicating the direction

of flow. The expansion joint must be installed in the system with

flow in the correct direction.

Flanged Assemblies ‐ These should be correctly aligned with their

mating flanges (vanstone flanges permit some rotational

misalignment). If a bellows is subjected to torsional forces due

to hole misalignment, then reduced cycle life and/or bellows

failure can occur.

Weld End Assemblies ‐ The bellows elements should always be

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protected during the welding process with flame retardant cloth or other shielding material. Weld splatter, arc strikes, or

cutting torch sparks can cause serious damage to the thin bellows element.

Final System Check ‐ After installation has been completed and shipping bars removed, check all anchors, guides, and

pipe supports. Slowly apply test pressure to the system, checking for any unusual movement of the bellows anchors or

guides. If movement is observed, immediately lower the pressure and re‐examine the system for damage.

NOTE: Unless otherwise specified, all expansion joints are designed for a test pressure of 1.5 times the design pressure.

Pr

UNRESTRAINED EXPANSION JOINTS: INSTALLATION GUIDELINES Axial Movement Single Bellows Assembly axial unrestrained expansion joints are not provided with attachments such as tie rods or

hinges to restrain pressure thrust. Therefore, they can be used only in a piping system that incorporates correctly designed

anchors and pipe alignment guides. These components prevent the bellows from over extension and damage due to

distortion under operating conditions.

Types of Anchors

MAIN ANCHORS are the most important to consider

from a design standpoint. They must resist the effects

of all forces acting upon them. These are pressure thrust,

bellows spring resistance, frictional resistance of pipe guides,

and inertial forces at bends and elbows.

INTERMEDIATE ANCHORS are used to divide a long

pipe run into shorter individual expanding sections, and

should be structurally capable of withstanding bellows

spring resistance and frictional forces only. Pressure

thrust forces at this juncture are completely balanced

and have no influence on the design of the anchor.

DIRECTIONAL ANCHORS permit movement in one direction

only. The movement is often parallel to the direction of the

lateral movement in installations where combinations of axial

and lateral movements are encountered.

PIPE ALIGNMENT GUIDES are another essential part of a properly designed piping system.

Thermal expansion in the system must be controlled so that the movement applied to the bellows

assembly is axial only. Pipe alignment guides must be designed so they prevent bowing and buckling

of the pipe. They should also keep frictional forces resulting from movement of pipe across the guide

to a minimum.

oblem

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CRYOGENIC APPLICATIONS (LNG)

The expansion Joints installed on cryogenic application could be of the same typologies showed

before.

The first important think is the material utilized that must be full construction on Stainless Steel. The

bellows could be also made on Inconel 625 LCF.

For this type of services, where possible it is preferable to utilize Expansion Joint external pressurized.

EXTERNALLY PRESSURIZED EXPANSION JOINTS

Externally Pressurized Expansion Joints

Externally pressurized expansion joints are utilized to compensate for large axial expansion of long piping systems. Macoga externally pressurized expansion joints are designed such that fluid/steam pressure acts on the outside of the bellows in addition to the internal surface of the bellows. The stabilizing effect of this external pressure increases the bellows ability to absorb long axial movements without the existence of squirm. This feature makes the externally pressurized expansion joint the best solution for many situations involving extensive axial movement.

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This uninsulated bellows coupling at the base of an LNG tank was accumulating ice balls and impairing the

movement of the stainless steel corrugations. The relative motion inherent to bellows necessitated the use of Proper insulation because it always remains flexible, even at cryogenic temperatures.

Expansion Joint applied on heat exchanger

1 Bellows installed over Shell

2 Bellows installed on tube side

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Disassembly joints

When considering the installation of valves, shut off gates and pumps etc. into a piping system it is particularly beneficial to include a Macoga disassembly joint along side each of these critical pieces of plant. During maintenance axial clearance is easily and quickly achieved in the pipe system to allow removal or replacement of your equipment by simply compressing the demounting joint with its threaded draw bars.

The following points are proven to be advantageous during long periods of operation:

• Plant efficiency is enhanced since the task of removing and replacing components is quicker, considerably reducing down time of intervention and loss of production.

• Macoga demounting joints are made entirely of steel. No rubber or plastic elements are used. Therefore there is no wear, aging or leakage.

• Macoga disassembly joints can be used up to 300°C taking into account the pressure reducing factor.

• Observations made over long operating periods indicate water loss reductions in the order of 15%.

• The excellent elasticity of the bellow allows it to absorb slight installation tolerances without creating leakage problems.

General During pipe installation, especially when components are to be replaced for servicing and maintenance, it is essential to leave an axial gap for easy installation of the units. The Macoga dismantling piece is completely maintenance free, ageing resistant and makes mounting and demounting considerably easier. Using the spring rate of the bellows, a gap is automatically generated while loosing the connection screws. Components can easily and quickly be removed. The other way round, a mounting gap previously set is closed by definitely restraining the bellows. As the movable component consists of a one-piece bellows, the Macoga dismantling piece remains 100% tight after as much mountings and demountings as you like. In the component itself, no supplementary seals are necessary. Only the piping components have to be provided with appropriate gaskets. Thanks to the extreme flexibility of the multi-ply bellows, a minor flange misalignment during pipe installation can be compensated without tightness problems. Possible radial divergences:

δ DN 500 = ca. ± 10 mm > DN 500 = ca. ± 5 mm During installation, the Macoga dismantling piece is at one side flanged to the pipe end and then, using the special tie rods, pulled to the components. In mounted position, the Macoga dismantling piece is restrained. While demounting the piece, only the connecting bolts must be released. The dismantling piece will spring back and generate automatically the gap, necessary for easy demounting and later reinstallation of the components.

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Reaction force When using unrestrained dismantling pieces, the following remarks are to be considered:

The bellows put under pressure tends to return in its smooth tube shape. A reaction force "F" is resulting, which can be

calculated with the help of the formulae in section EJMA code. This reaction force must be compensated by the pipe

construction, or taken in account by the layout of the anchor points. If axial movements occur, the spring rate has also to be

considered.

Underground installation Macoga dismantling pieces are suitable for underground installation when equipped with outside protection sleeves. Execution

• Without tie rods, not for/ for underground installation.

With this solution the end thrust pressure must be taken by other pipe components.

With tie rods, not for/ for underground installation With this solution the end thrust pressure is taken from the dismounting joint.

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Example of Special application : Bellows installed on Valve